How do UV texture seams work?
UV unwrapping is an art… Some things that have helped me:


In “Object Mode” apply the scale Ctrl + A then select “SCALE” from the drop down menu Before you attempt to unwrap the mesh.
In general seams are placed on object edges. The order of their selection shouldn't matter.
After unwrapping you can move/rotate individual maps. Easily selectable by selecting one vertice of the UV map then Ctrl + L to select the rest of the linked vertices.
Try unwrapping using “Smart UV Project” with the “Angle Limit” set to “89” (Doesn’t always help).
Unwrap the mesh and then export the UV layout. Found under UVs then at the top of the drop down menu “Export UV Layout”. Bring the exported UV layout into Photoshop or Gimp and place your textures there.
In a pinch assign a different Material to the mesh faces for each Texture.
This simple tutorial helped me to begin to understand UV unwrapping.
https://www.youtube.com/watch?v=fDABx8wWGR4